The load in an elevator car of a traction elevator system has been used by the car and/or group supervisory control for such control strategy functions as controlling by-passing of hall calls, initiating the start of the "next" car from a building lobby, initiating system "down peak", initiating special floor features, susch as convention floor strategy, and the like.
Unbalanced car load, i.e., a load, or lack of load, which either causes the weight on the car side of the traction ropes to exceed the weight on the counterweight side, or vice versa, has been detected and used to improve car dynamics, such as for providing smoother car starts and more accurate and faster landings.
The drive related compensation signals, related to unbalanced load, and the supervisory signals, related to actual car load relative to rated car load, are usually independently obtained.
A common arrangement for obtaining the supervisory signals resiliently mounting the car platform and measuring the platform deflection or position. While this is accurate enough for supervisory purposes, the non-linearity of the platform isolation material, as well as permanent deformation of such materials due to ageing, introduce errors which would adversely affect car dynamics. Also, car load alone may not accurately reflect unbalanced torque in every instance, as the weight of the hoist ropes may not be compensated for; or, even when compensation is provided for the weight of the hoist ropes, it will usually have an error, which error is dependent upon car position in the building.
Thus, it would be desirable to be able to derive car loading signals for both supervisory and motor control functions from car platform position, if the hereinbefore mentioned problems associated with hoist rope compensation error and the non-linearity and aging of platform isolation materials can be satisfactory solved.